Amongst the previous uses given to nanoparticles composed of a dielectric nucleus and a metal shell, different research groups worldwide have used them in medicine for the thermal ablation of tumour cells: they are injected in a tumour and a laser in the near-infrared region (NIR), with the wavelength whereat the particles are absorbed and diffracted, is externally applied; the particles are heated, resulting in the death of the tumour tissue due to temperature elevation, as reflected in patents US2002103517-A1 and U.S. Pat. No. 6,530,944-B2, and in several popular science documents.
Some types of nanoparticles have also been patented as filling material for paints, to obtain thermal insulation paints, as disclosed in U.S. Pat. No. 6,344,272-B1 held by UNIV RICE WILLIAM MARSH.
Also well-known are their plasmon optical resonance properties, which make them of interest to be used as contrast agents in medical .imaging (by means of photoacoustic tomography), and their use is disclosed in various documents, such as patents US2002187347-A1 and U.S. Pat. No. 7,144,627-B2. They have also been used to activate an optically activated sensor in patents US2004214001-A1 and U.S. Pat. No. 7,371,457-B2.
Other similar applications also consider the use of nanoparticles as optically activated valves; this use is reflected in documents such as Optically controlled valves for microfluidics devices. Sershen, S R., Ng, M. A., Halas, N. J., Beebe, D., West, J. L. Advanced Materials, 17 (2005): 1366-1368.
Currently, there are other inorganic nanoparticles the use whereof is aimed at optical labelling. However, these nanoparticles are based on carbon (e.g. carbon nanotubes) or quantum dots (semiconductor nanostructures that confine the movement, in the three spatial directions, of conduction band electrons, valence band gaps or excitons (binding pairs of conduction band electrons and valence band gaps, CdSe, CdS, CdTe, etc.)) (e.g. ©Evident Technologies, Inc.). Said materials emit at a single wavelength within the near-infrared region.
Invention patent US20070165209 discloses a method and a device for applying security labels or identifiers to documents or banknotes in order to prevent the counterfeiting thereof. Said identifiers may have the form of nanolabels, which may be Raman-active metal nanoparticles.
More specifically, gold nanoparticles may heat an area of up to 1000 times their size when they are excited with a laser of a given wavelength. Said property has been used to produce the photothermal ablation of tumours in vitro and in vivo, as previously mentioned. These nanoparticles are formed by a dielectric nucleus (silica) and a shell made of gold or any other noble metal (i.e. silver, platinum, copper). By changing the relative dimensions between the materials that make up the nucleus and the shell, it is possible to modify the properties of the resonant plasmon (wavelength of optimal optical extinction) of gold, causing them to absorb light in the near-infrared region (NIR). This near-infrared region (between 800 and 1200 nm) is of interest in biomedical applications, since tissues are transparent in said region, and do not absorb light from the incident beam. It is the so-called “water window”. Thus, if a tissue is irradiated with any laser of a wavelength within that range, the temperature of said tissue will not rise. However, if the tissue is infiltrated with gold/silica nanoparticles, the application of a laser in the area would cause cell death by hyperthermia. Some authors have studied the effect .of different nanoparticle geometries and shapes/thicknesses on the absorption of IR radiation, but always from the standpoint of biomedical use, in phototherapy and thermal ablation.